The X-ray Sun

This picture of the Sun was taken on January 24, 1992. The image
shows the Sun at X-ray wavelengths and it was recorded by the
Soft X-ray Telescope on the Yohkoh (which means "Sunbeam"
in Japanese) satellite. The bright areas are where the Sun's magnetic fields
are strong enough to trap the very hot gases in the corona of the Sun. The
fields are not strong enough to do this at the poles of the Sun. Notice
that the surface of the Sun is dark: the X-rays Yohkoh records are from
gases which are heated to millions of degrees. The surface of the Sun is much
cooler than this, so it appears dark.